Both companies are playing catch-up with the likes of Facebook, which offers four months of paid leave. Its chief executive, Mark Zuckerberg, had his own announcement to make in recent days: He and his wife are expecting their first child.

For all the good that may come from the new policies at Netflix and Microsoft, Mr. Zuckerberg may have the biggest opportunity to help members of the paternity fraternity by using every last day of his leave. Without prominent men in high-performing organizations making parental leave the default choice, the mainstreaming of paid leave for fathers will take a lot longer.

Paid paternity leave is an incredible privilege for employees in the small number of companies that offer it, and keeping the paychecks coming helps a lot. Cultural hurdles, however, are far harder to clear. Taking a lengthy paternity leave in a company where few, if any, senior men have ever done so requires a fair bit of courage. And while some employers believe that generous maternity leave more than pays for itself in retention, there is little proof that male employees won’t experience a career stall immediately afterward if they dare to step out for a while.

This evidence cannot emerge without employers offering paid paternity leave in the first place, and most of the people (generally older, often men) who sign off on these policy changes generally haven’t seen fit to do so. Only 17 percent of the employers that the Society for Human Resource Management surveys provide fathers with the benefit.

Employers that do so tend to be clustered in industries like technology, finance and professional services. Yes, the rich get richer, though it stands to reason that employers who already pay generously would lead the pack here. There are real productivity losses and recruiting costs they would otherwise bear in having bleary-eyed employees roaming the halls and others quitting altogether to stay home with new children. California, New Jersey and Rhode Island require some paid parental leave to all new parents; payroll taxes provide the funds.

Netflix and Microsoft are on the outer edge of generosity, as you can see from the chart accompanying this column. There, I list the most generous employers I could find. If I missed yours, please post a comment and let me know because I’ll be regularly updating the chart.

The unlimited leave at Netflix appears to be unprecedented among large employers in the United States, though it’s anyone’s guess as to what the average length will turn out to be. The company did not try to model it out before its announcement.

Employers that consider offering unlimited vacation time tend not to go through with it, according to their consultants. “Their concern is that if they don’t tell their employees two weeks or four weeks, then it will be fuzzy and usage will go down,” said Rich Fuerstenberg, senior partner for Mercer’s health and benefits business.

New fathers at Microsoft will now get 12 weeks of paid leave, identical to what mothers get (though the women may also be eligible for an additional eight weeks of disability pay). This equality stands in contrast with an odd requirement at other employers, where they ask you to declare yourself the “primary” caregiver before you qualify for the most generous paid leave. The secondary parent gets less paid time off.

No in-home audits are required, but every expert I spoke to disapproved of classifying commitment in this way. “I find it to be a very weird rule,” said Kenneth Matos, senior director of research for the Families and Work Institute. “It goes back to this concept where there is someone who is doing the work and someone else who is hanging out and on vacation.”

Whatever the label, there’s no escaping the fact that the small number of men taking paternity leave at most employers so far means that many colleagues will remember their absence long after they return. So what’s the upside to paternity leave, besides the bonding time (which is essential for single parents of either gender)?

For men with spouses, it means that the couple is learning to raise their new child together, as opposed to there being one parent (usually the mother) figuring it out and then instructing the other. “Having men be more engaged means that they don’t have to do it all themselves,” said Mr. Matos, who added that taking equal leave is also an investment in your relationship with each other.

Academic research, set mostly in Europe, provides additional evidence of how paternity leaves help mothers. In Norway, women are absent from work less because of sickness if their husbands take longer leaves. In France, mothers are less likely to experience depression. Among the Swedes, each month of parental leave appears to increase mothers’ earnings by 6.7 percent, perhaps by helping her focus completely on work once she returns.

Widespread, lengthy paternity leaves also have the potential to help female colleagues. Mr. Fuerstenberg of Mercer points out that some bosses may look at a woman and a man of childbearing age and favor the male for a promotion because of concern about the woman taking a six-month maternity leave. “If you provide the same benefit to both people and encourage both to take the leave, there is no opportunity for bias,” he said. Yes, there are plenty of opportunities for gender bias elsewhere, but the expectation of equal length leaves could only help.

Selflessness aside, however, what happens to a father’s career after a lengthy paternity leave? In Europe, women who take long parental leaves may suffer career consequences, as my colleague Claire Cain Miller reported last year.

In the United States, we don’t know all that much yet about men specifically. Google has had generous parental leaves for several years and crunches plenty of its own human resources data. The company would not tell me whether it had specifically matched up men who took long parental leaves against otherwise similar men who did not, to see whether the leave-takers suffered financially in the years afterward.

But Roya Soleimani, a Google spokeswoman, did offer some encouraging words. “I can assure you that all levels of analysis are rigorously done by our team to ensure that there isn’t bias,” she said. “We see no sign of bias in our people processes, which includes compensation, promotion, performance.”

Your employer may be nothing like Google, so there’s no denying that paternity leave requires bearing some risk. But it is also something that you can do for your fellow man, literally. If people don’t use the leave, employers will take it away or cut it back or not extend it.

Moreover, bias against leave-takers probably won’t go away entirely until there are men in positions of authority who have taken it themselves. Right now, most new fathers are left to hope that their bosses won’t grumble (rightfully) about the fact that they didn’t get to go on a long, paid leave or (rightfully again) about the fact that they probably aren’t getting 12 weeks of paid time off to take care of an aging parent.

Employers can try to head off any such resentment by ordering managers to meet with fathers planning a leave the same way they do with pregnant women. “We encourage them to adjust their goals for that period of time,” said Mary Tavarozzi, North America practice leader for absence and disability management at Towers Watson. “Then, employees don’t feel like they’re going to get dinged on performance reviews because they had the same goals as a guy who had been there all 12 months with no leave.” Initiate that discussion yourself if no one at your employer does.

Still, the normalization of paternity leave can only happen when larger numbers of men publicly declare their intention to take one and then shout from the rooftops about how spectacular it was. So let me do my part right here: My byline will be scarcer in the coming months as I take my own paternity leave. I’ve done it before, and I feel intensely lucky that I’m able to do it again.

As for Mr. Zuckerberg, he is a busy man, and who knows how Wall Street would react if he sat out a quarterly earnings call or two? Here’s hoping, though, that we’ll get to find out.